'86 Vintage C6.. Dexron or Type F?

I have a C6 from an 86 E350 with 64K miles. As far as I can tell it's never been opened (the plastic plug was still in the pan). I replaced the filter, front and rear seals, pan gasket, and backed off the band adjustment several turns and adjusted it to spec.

Usage is just daily driver type stuff behind a very mild 460 in a 78 Cougar.

Dipstick says "Dexron II". I was going to stick with Dex/Merc. Valvoline makes a 'high mileage' fluid I used to resurrect a 15 year old trans that had 30K miles, and works great.



Any reason not to, in this particular case?

go with type F it will firm up the shifts
Frank

Thanks Frank.